I do have some about 9" long in bigger sizes (like 7 and up) that I use for things like hats or whatever that use larger yarn, but the ones I use for socks, mittens etc. are all 7" and they work well for me. I don't have any of the little short ones, but wouldn't mind having some sometimes.

More needles.
Better too long, I think, than too short through so it is up to you.